LSAT Logical Reasoning cheat sheet

LSAT Logical Reasoning: Core Reference

• Argument structure: conclusion = the claim the author wants accepted; premises = stated support; background = context with no support role. Ask "what does the author want me to believe, and what is offered in its favor?"

• The conclusion is often signaled by therefore, thus, hence, so, clearly, must be, or by contrast with a "some say / critics claim" clause that precedes it.

• Assumption (necessary) test: negate the answer choice. If the negation makes the argument collapse, the choice is required; if the argument survives, it is not required.

• Sufficient assumption test: add the answer choice to the premises. If the conclusion follows deductively, the choice is sufficient; it need not be something the author believed.

• Flaw questions: the credited answer names the specific gap between premise and conclusion (e.g., treats correlation as causation, ignores an alternative explanation, equivocates on a term, generalizes from an unrepresentative sample).

• Strengthen/Weaken: predict the direction of the gap first. A weakener makes the conclusion less likely without needing to disprove it; a strengthener closes the gap or rules out a rival cause.

• Must Be True / Most Strongly Supported: accept only what the stimulus proves. Answers that are plausible, useful, or consistent with the stimulus but not entailed are wrong.

• Parallel reasoning: match the abstract structure (premise types, quantifiers, conclusion strength) rather than topic. Parallel flaw requires matching the error, not just the form.

• Question-stem keywords set the task: "if true" = treat the choice as given; "best supported" = inference; "required" = necessary; "most seriously weakens" = one answer damages the argument more than any other.